This invention relates to a process for the manufacture of the hydrofluorocarbon 1,1,3,3,3-pentafluoropropene (HFC-1225zc). HFC-1225zc can be made from the dehydrochlorination of 1-chloro-1,1,3,3,3-pentafluoropropane (HCFC-235fa). Alternatively, HFC-1225zc can also be made from the dehydrofluorination of 1,1,1,3,3,3-hexafluoropropane (HFC-236fa). The dehydrochlorination and/or dehydrofluorination may be conducted by reaction with a caustic solution, or by thermal decomposition of HCFC-235fa and/or HFC-236fa, with or without a catalyst.
Chlorofluorocarbons (CFCs) like dichlorodifluoromethane have been used as refrigerants, blowing agents and diluents for gaseous sterilization. In recent years, there has been widespread concern that certain chlorofluorocarbons might be detrimental to the Earth's ozone layer. As a result, there is a worldwide effort to use halocarbons which contain fewer or no chlorine substituents. Accordingly, the production of hydrofluorocarbons, or compounds containing only carbon, hydrogen and fluorine, has been the subject of increasing interest to provide environmentally desirable products for use as solvents, blowing agents, refrigerants, cleaning agents, aerosol propellants, heat transfer media, dielectrics, fire extinguishing compositions and power cycle working fluids.
In this regard, 1,1,3,3,3-pentafluoropropene (HFC-1225zc) is a compound that has the potential to be used as a low GWP (Global Warming Potential) refrigerant, blowing agent, aerosol propellant, solvent, etc, and also as a fluorinated monomer. Currently this material is not available in large quantities. There is no commercially viable large scale process for manufacturing this HFC. However, the raw materials to make HFC-1225zc are readily commercially available, and this invention provides a process technology that allows for the manufacture of HFC-1225zc in large commercial scale. It is known that one can produce HFC-1225zc in a high temperature hydrogenation process using 2-chloro-1,1,3,3,3-pentachloropropene (CFC-1215) or 2,2-dichloro 1,1,1,3,3,3 hexafluoropropane (CFC-216) in the presence of a metal catalyst. The organic raw materials for these processes are not readily available. U.S. Pat. No. 5,714,654 has been proposed for producing 1,1,3,3,3-pentafluoropropene, in which 2-chloro-1,1,3,3,3-pentafluoropropene is hydrogenated at a temperature between 30° C. and 450° C. in the presence of a palladium, platinum and rhodium catalyst, or in which 1,1,1,3,3-pentafluoro-2,3-dichloropropane is dechlorinated by using hydrogen in the presence of a metal oxide catalyst. U.S. Pat. No. 6,369,284 provides a process for producing 1,1,3,3,3-pentafluoropropene (HFC-1225zc) from 1,1,1,3,3,3-hexafluoropropane (HFC-236fa). In accordance with this patent, HFC-236fa is dehydrofluorinated to HFC-1225zc over a catalyst at a temperature of from about 200° C. to 500° C. The catalyst system is a combination of oxides, fluorides and oxyfluorides of magnesium, zinc and mixtures of magnesium and zinc, lanthanum fluoride, fluorided lanthanum oxide, and three-dimensional matrix carbonaceous material. U.S. Pat. No. 6,031,141 also shows a process for producing HFC-1225zc from HFC-236fa using a cubic chromium trifluoride catalyst.
It has been determined that these known processes are not economical relative to their product yield. Accordingly, the present invention provides an alternate process for forming HFC-1225zc which is more economical than prior art processes and a higher yield process as compared to known processes. In particular, it has now been found that HFC-1225zc may be formed by dehydrochlorination of HCFC-235fa using caustic or thermal decomposition optionally in the presence of a catalyst for HCl removal. Alternatively, HFC-1225zc may be formed by dehydrofluorination of HFC-236fa using caustic or thermal decomposition optionally in the presence of a catalyst for HF removal.